Re: [PATCH/RFC RESEND] leds: Use set_brightness_work for brightness_set ops that can sleep

[Jacek Anaszewski]

On 07/01/2015 09:43 AM, Pavel Machek wrote:
> On Wed 2015-07-01 09:28:52, Jacek Anaszewski wrote:
> > On 06/30/2015 07:46 PM, Pavel Machek wrote:
> > > On Tue 2015-06-30 15:06:19, Jacek Anaszewski wrote:
> > > > On 06/30/2015 01:58 PM, Pavel Machek wrote:
> > > > > On Tue 2015-06-30 10:01:08, Jacek Anaszewski wrote:
> > > > > > This patch rearranges the core LED subsystem code, so that it
> > > > > > now removes from drivers the responsibility of using work queues
> > > > > > internally in case their brightness_set ops can sleep.
> > > > > > Addition of two flags: LED_BRIGHTNESS_FAST and LED_BLINK_DISABLE
> > > > > > as well as new_brightness_value property to the struct led_classdev
> > > > > > allows for employing existing set_brightness_work to do the job.
> > > > > > The modifications allow also to get rid of brightness_set_sync op,
> > > > > > as flash LED devices can now be handled properly only basing on the
> > > > > > SET_BRIGHTNESS_SYNC flag.
> > > > >
> > > > > Are you sure this is good idea?
> > > > >
> > > > > You'll now use single callback for blocking and non-blocking
> > > > > behaviour. I'm pretty sure stuff like lockdep will have some fun with
> > > > > that.
> > > >
> > > > I enabled "Lock Debugging" options and didn't get any warning.
> > > > Could you describe the use case you are thinking of?
> > >
> > > You may get one when one of the sleeping functions uses some lock...
> >
> > Drivers which use spin_lock in their brightness_set op will have to
> > set LED_BRIGHTNESS_FAST flag, which will instruct the LED core to
> > call the op synchronously. On the other hand drivers which can sleep
> > in their brightness_set op won't set the flag, which will make LED core
> > delegating the op to the work queue task. It is also possible that
> > driver with brightness_set op that can sleep set SET_BRIGHTNESS_SYNC
> > flag - then LED core will call it in a synchronous way from
> > led_brightness_set and it will schedule work queue task in case
> > the op is called from triggers.
>
> I understand this "works".
>
> > If you want to NAK the patch, please come up with detailed analysis
> > on how it can cause problems. Without this I infer that you didn't
> > spend a second on analyzing the code. This is counterproductive.
>
> NAK.
>
> Because calling two functions with different semantics through same
> function pointer is extremely ugly, and _will_ cause lockdep
> problems. Talk to the lockdep people for details.

Which two functions are you thinking of? There is a single
brightness_set op to call.

--
Best Regards,
Jacek Anaszewski
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